This invention relates generally to blood pressure monitoring, and more particularly to a method and apparatus for automatic non-invasive blood pressure monitoring.
Blood pressure may be measured non-invasively using a cuff applied to an upper or lower extremity, such as the upper arm, for example, that is inflated and deflated to yield a numeric display of systolic, diastolic and mean blood pressure. The method applied using a cuff is referred to as the oscillometric method, since oscillations in the arterial walls created by cardiac contractions are detected. Different cuff sizes are used to accommodate patients of different sizes. If the cuff size is too small for the patient size, it will cause the non-invasive blood pressure (NIBP) monitor to read falsely high. Conversely, too large a cuff can lead to falsely low readings. Thus, a given monitor must be capable of accepting cuffs of different sizes, which are designed so that they can be detached from the monitor. To properly apply the oscillometric method using a cuff, the air within the cuff must be expelled before taking a measurement, since residual air can lead to inaccurate readings caused by a loose-fitting cuff. Additionally, the hose connections between the cuff and the monitor must be checked for air leakage, which can also lead to inaccurate readings.
Present NIBP monitoring systems include both manual and automatic systems. Manual systems typically have manual inflation bulbs and manual deflation valves, which may be found on mercury and aneroid sphygmomanometers, for example, while automatic systems typically have microprocessor controlled cuff inflation systems and electronic read-out units. Some automatic systems also include automatic cuff deflation systems, which are typically controlled by an electronic valve within the monitor. Electronic deflation valves are more costly than manual deflation valves, and large-orifice electronic deflation valves are substantially more costly. To keep the cost of the automatic NIBP monitor at an acceptable level, small-orifice electronic deflation valves, or no deflation valves, are employed. Where a small-orifice electronic deflation valve or no deflation valve is used, a user may resort to manual squeezing of the cuff, or complete detachment of the cuff hose from the monitor, in order to quickly deflate the cuff, which may add wear and tear to the cuff and hose and is typically considered an inconvenience to the user.